Our long-term goal is to identify key epigenetic regulator(s) that modulate acute kidney injury (AKI) and chronic kidney disease (CKD). Specifically, we will investigate the role of enhancer of zeste homolog 2 (EZH2), a histone methyltransferase that acts primarily as a gene silencer, in the pathogenesis of acute and chronic kidney injury and assess whether pharmacologic and genetic targeting of EZH2 can prevent or ameliorate AKI and CKD. AKI and CKD are common and costly global health problems. AKI predisposes to CKD; CKD increases the risk of cardiovascular disease and death. At present, there are no effective therapies for AKI. Current treatments for CKD retard but not prevent progression to end stage renal disease. Identifying key molecules that mediate and modulate AKI and CKD is imperative to develop new, more effective therapies to prevent and treat AKI and halt progression of CKD. In preliminary studies we found that EZH2 is highly expressed in the kidney after acute and chronic injury and that inhibition of EZH2 with 3-DZNeP attenuates development of renal fibrosis induced by unilateral ureteral obstruction. This is associated with preservation of PTEN and Smad7 expression and inhibition of epithelial cell cycle arrest in G2/M phase. Importantly, EZH2 inhibition also improves renal function and reduces renal tubular cell injury and apoptosis in ischemia/reperfusion (I/R) induced AKI in mice. These data establish EZH2 activation as a critical factor in the pathogenesis of acute and chronic renal injury. However, the molecular basis by which EZH2 mediates these pathological processes remains poorly understood. Our central hypothesis is that upon injury, EZH2 promotes the progression of AKI to renal fibrosis by inducing renal tubular death and defective renal epithelium repair. Our working hypothesis is that injury to renal tubular cells activates EZH2 leading to epigenetic repression of multiple genes associated with cell survival, promoting cell death. Prolonged EZH2 activation in surviving tubular cells results in partial EMT, G2/M arrest, a secretory profibrotic phenotype by repression of E-cadherin, PTEN and Smad7 and subsequent activation of some profibrotic signaling pathways such as Smad3. To test this hypothesis, we will first define the role of EZH2 in the pathogenesis of AKI and progression of AKI to CKD by using more specific EZH2 inhibitors and conditional knockout mice with EZH2 deleted in renal tubular cells following I/R and folic acid injury; Second, we will elucidate the mechanism(s) linking EZH2 activation to renal epithelial cell death by examining the relative contributions of E-cadherin, tissue inhibitor of metalloproteases-3 and Raf-1 kinase inhibitor protein to renal epithelial cell death in vitro in the presence or absence of EZH2 inhibition. Finally, we will determine the molecular basis of EZH2- mediated transition of renal epithelial cells to a profibrotic phenotype by examining the relative contributions of E-cadherin, PTEN and Smad7 to partial EMT and G2/M arrest, leading to a secretory profibrotic phenotype in cultured renal epithelial cells following injury with aristolochic acid. Successful completion of this study will increase our understanding on histone methyltransferase?mediated epigenetic regulation in acute and chronic kidney injury and establish the utility of pharmacologic targeting of EZH2 as a potential novel therapy for AKI and CKD.